Ventilator for intensified breathing and valve in patient conduit of apparatus for intensified breathing

ABSTRACT

A ventilator for intensified breathing that includes a single safety valve arranged in the gas mixture and inhalation conduit assembly. The single safety valve includes a restrictor valve for overpressure in the breathing system, a valve that allows breathing from the atmosphere, and a directional valve for inhalation. The safety valve is arranged and controlled by an electronic control system of the ventilator.

BACKGROUND OF THE INVENTION

The invention relates to a ventilator, according to the preamble ofclaim 1, for intensified breathing and to a valve, according to thepreamble of claim 19, arranged in a patient conduit of an apparatus forintensified breathing.

Ventilators are used for intensifying the breathing of patients whoseown breathing activity for some reason is inadequate. They are typicallyapplied to patients anaesthetised and relaxated during surgery and tothose in intensive care. A conventional ventilator provides a cyclicventilation of lungs. The main phases of a cycle are inhalation andexhalation. A cycle recurs at a desired, controllable pace. A ventilatorat its simplest is primarily in accordance with the preamble of claim 1,the needed pressure being provided e.g. by means of a blower.

Inhalation gas in high power ventilators is most often a mixture ofoxygen and nitrogen, whereby an oxygen concentration can be arranged asdesired between 21 to 100%. For the controlling of the mixture,ventilators are connected to two pressure tanks. The pressure in thepressure tanks is first brought to a constant level by pressureregulators. The bringing of the pressure to a constant level in thepressure tanks improves, on one hand, the adjustability of flow andreduces, on the other, the requirements set for inhalation valves usedfor controlling the gas flow in a particular conduit. The gas flows ofthe conduits are arranged to provide the above mentioned oxygenconcentration in the mixture and a desired total flow. The total flowcan be either a parameter determined directly by the operator or adesired flow value indirectly calculated by a control system from otherparameter settings and/or measurement signals. The control systemcontrols the inhalation valves by comparing a measurement signalproportional to the prevailing gas flow to the desired gas flow and bychanging the control settings when needed. In the described system saidmeasurement signal is a flow measuring element, but it can also be alocation detector of a closing element of an inhalation valve, apressure signal, a signal proportional to temperature, or a combinationof these.

After the separate gas flows are measured and adjusted, the flows arecombined and a gas mixture is produced. At this stage the pressure ofthe gas mixture measured from an inhalation conduit is in most cases,with sufficient accuracy, the same as it is when delivered to a patient.Said pressure can thus participate also in the determining of saiddesired gas flow, if the control system has been arranged to adjust aconstant pressure delivered to the patient during inhalation. Thepressure in the inhalation conduit is measured as a difference pressurein relation to the surrounding air pressure. Other functions included ina module comprise a measurement of the oxygen concentration of themixture, which can, however, also be located closer to the patient.

From the gas mixture module the gas flow is conveyed along theinhalation conduit to a Y piece, to a second branch of which the patientis connected either through a breathing mask or an intubation tube, athird branch being connected to an exhalation conduit. Inhalation thustakes place by means of an over-pressurised gas mixture delivered fromthe pressure tank through the inhalation valve to the inhalationconduit, whereby the pressure in the inhalation conduit increases. Anexhalation conduit is at the time kept closed by an exhalation valve, sothe gas mixture is further conveyed to the lungs, causing also a rise inpressure there.

Exhalation takes place spontaneously when an over-pressure stored in thelungs during inhalation is released. This is achieved by the a closingof the inhalation valve(s) and by the opening of the exhalation valve inthe exhalation conduit, whereby the pressure of the inhalation andexhalation conduits acting on the patient decreases. The over-pressurein the lungs is thus released as a gas flow through the exhalationconduit. The control system controls the exhalation valves and, whennecessary, also the inhalation valves in such a way that the pressurelevel of an exhalation period is reached as quickly as possible and thenkept as constant as possible. For adjusting the pressure of theexhalation period, the ventilator is often provided with a pressuresensor arranged in the exhalation conduit, although in most cases thepressures of the exhalation and the inhalation conduits come very closeto each other.

Modern ventilators make full use of the opportunities offered byelectronics for controlling a breathing cycle according to settings. Thecontrol is performed by arranging the inhalation and exhalation valvesto implement parameter settings. These settings include inhalationover-pressure, exhalation over-pressure, inhalation volume and theduration of inhalation and exhalation efforts.

Since a ventilator is a life-supporting apparatus, it must be safe. Thisrequirement for safety means that the apparatus must not cause danger toa patient or to a user during normal operation or in the case of asingle malfunction. To ensure this, the ventilator is to be providedwith safety circuits, which do not depend on its basic functions andwhich are activated when a basic function for some reason malfunctions.One of the most critical emergencies a ventilator can cause to a patientis over-pressurisation of the lungs. Over-pressure can damage the lungsin a very short time. Malfunction that can cause an over-pressure canoccur e.g. when the exhalation valve is blocked to a closed position orthe inhalation valve remains open. In order to prevent damages also insuch cases of malfunction a restrictor valve is typically arranged inthe ventilators. It is usually located in the gas mixture inhalationconduit.

Prior art comprises two types of functions restricting over-pressure.The more conventional one is a spring-loaded valve. The spring iscalibrated to open at a predetermined constant pressure. A typicalcalibration pressure varies from 10 to 12 kPa. A constant limit pressuredoes not, however, guarantee a fully sufficient safety circuit,considering the varying needs of patients in intensive care. Forpatients in critical condition over-pressure can cause danger evenbefore said limit pressures are attained. Another weakness in saidsafety valve is that it only releases an over-pressure higher than thecalibrated pressure limit and in case of a malfunction the patientremains over-pressurised at said pressure limit, instead of the pressuredropping to the level of a normal exhalation pressure.

A more advanced version of this safety valve is to replace thecalibrated spring with a control system. This control system keeps thevalve closed either electronically or electro-pneumatically. Anadvantage the control system provides is that it allows the limitpressure to be set according to the patient's needs and, on the otherhand, over-pressure to be fully released to the level of the exhalationpressure. The control system for an over-pressure valve comprises apressure-sensitive element. A signal transmitted by this element iscompared with a predetermined limit pressure. When the signal exceedsthe limit pressure, the control system opens the restrictor valve of theover-pressure.

Another security feature associated with ventilators used particularlyin intensive care is that they allow spontaneous breathing. Although thepatients are connected to ventilators, they are often capable ofbreathing independently and they are allowed to do so. A breathing gasis usually mixed by inhalation valves with a desired oxygenconcentration. Should the mixing system become damaged, the prior artsolutions open the inhalation conduit to the environment, allowingspontaneous breathing to be continued from the atmosphere. Theinhalation conduit is opened using either a separate valve or thefunction is combined with said over-pressure restrictor valve.Irrespective of the method of implementation, it is vital for the normaloperation of the ventilator that the valve closes tightly when it is notneeded to open, because any leaks would make the gas intended for thepatient to flow out, which reduces the patient's breathing volume,causing other critical situations and leak alarms. The probability ofleaks naturally grows as the number of opening components in thebreathing conduits increases. The apparatus also needs to be cleanedafter each patient and the accumulation after cleaning becomes morecomplex, increasing thus the probability of error.

A supplementary requirement associated with spontaneous breathing is toavoid return breathing, i.e. the mixing of exhalation and inhalationgases. Inhalation and exhalation gases are conveyed to different flowconduits by directional valves arranged in said conduits. In prior artsolutions these valves are typically placed in the gas mixture moduleand in the exhalation valve module. The basic requirement set for thesevalves is small gas flow resistance to reduce the patient's breathingeffort. In the inhalation conduit the directional valve is to be locatedbetween the patient and the point of opening of the inhalation conduit.In prior art systems with a combined opening for the inhalation conduitand the over-pressure restrictor valve said directional valve can causedanger when the directional valve prevents gas flow from the patient tothe over-pressure restrictor valve, i.e. the function for which saidvalve is arranged in the apparatus.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to eliminate above describedshortcomings. This is achieved with a ventilator and a valve of theinvention, which are primarily characterized in that a closing elementis arranged in a safety valve in such a way that it remains in a closedposition at least partly by the impact of gravity, whereby said safetyvalve also provides a directional valve for inhalation, which closesduring exhalation the connection to the atmosphere.

When the closing element is arranged in a valve housing for asubstantially vertical movement, the valve remains under normalconditions in a closed position primarily from the impact of gravity,whereby any supplementary means closing the closing element can be madesmall in size and in power, which for its part reduces the size of theentire safety valve.

The closing element preferably comprises a part, which is of as smallvolume but as large surface as possible and e.g. in the form of a plate,cone or ball and which seals against a seat. This kind of closingelement structure is advantageous for the closing of the valve when thebreathing gas is delivered from a pressure tank and, on the other hand,it makes spontaneous breathing easy when the apparatus is released froman active mode.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention will be now described in greater detail with reference tothe enclosed drawings, in which

FIG. 1 illustrates an operational block diagram of a ventilator of theinvention used in intensive care and the connection of a patientthereto,

FIG. 2 illustrates a cross-section of a safety valve of the invention ina closed position,

FIG. 3 illustrates a valve of FIG. 2 in an open position,

FIG. 4 illustrates a valve of the Figure as seen from above,

FIG. 5 illustrates an alternative embodiment of a safety valve of theinvention,

FIG. 6 illustrates another alternative embodiment of a safety valve ofthe invention, and

FIG. 7 illustrates a further alternative embodiment of a safety valve ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION

A ventilator shown in FIG. 1 comprises a compressed oxygen interface 2,including a compressed oxygen conduit 3, to be connected to a compressedoxygen tank 1; a compressed air interface 5, including a compressed airconduit 6, to be connected to a compressed air tank 4; a gas mixtureconduit 7, where the compressed oxygen and the compressed air conduits 3and 6 are joined; an inhalation conduit 8 as an extension of a gasmixture conduit 7, said inhalation conduit being connected to a branch10 of a Y piece 9, other branches of the Y piece 9 being a patientbranch 11 and a branch 12 leading to an exhalation conduit 13 of theventilator.

In conduit 3 are arranged a pressure regulator 14, a flow measuringelement 15 and an inhalation valve 16 and, correspondingly, in conduit 6a pressure regulator 17, a flow measuring element 18 and an inhalationvalve 19.

The pressure regulators 14 and 17 are used for providing constant levelof pressure in pressure tanks 1 and 4, which improves flow adjustabilityand reduces the requirements set for inhalation valves 16 and 19 usedfor controlling the flow in conduits 3 and 6.

In a gas mixture and inhalation conduit assembly 7, 8, in turn, arearranged a pressure measuring element 20, a safety valve 21, which willbe later described in detail, and an oxygen concentration measuringelement 22.

An exhalation conduit 13 is provided with a pressure measuring element23, an exhalation valve 24 and a flow measuring element 25.

A patient P is connected to the branch 11 by a breathing mask or anintubation tube (not shown in the drawings), inhalation being performedby an over-pressured gas mixture delivered of pressure tanks 1 and 4through the inhalation valves 16 and 19 to the inhalation conduit 8,whereby pressure in the inhalation conduit 8 rises. The exhalationconduit 13 is kept closed by the exhalation valve 24, so the gas mixtureis conveyed further to the lungs of the patient P, causing also a risein pressure there.

Exhalation takes place spontaneously by the releasing of theover-pressure stored in the lungs during inhalation. This is achieved bythe closing of the inhalation valves 16 and 19 and by the opening of theexhalation valve 24, whereby the impact of the pressure of theinhalation and exhalation conduits 8 and 13 acting on the patient Preduces. The over-pressure in the lungs then discharges in the form of agas flow through the exhalation conduit 13.

The arrangement shown in FIG. 1 further comprises a control system 26,which receives information over paths 27, 28 and 29 from flow measuringelements 15, 18 and 25; over paths 30 and 31 from pressure measuringelements 20 and 23 and over a path 32 from an oxygen concentrationmeasuring element 22. On the basis of the measurement data received, thesystem 26 controls, when necessary, the inhalation valves 16, 19 overthe paths 33 and 34; the exhalation valve 24 over the path 35 and thesafety valve 21 over the path 36.

It is also to be noted that in the above described system the locationof the pressure measuring elements 20 and 23 is not essential and atleast the flow measuring elements 15 and 18 can in some cases possiblybe left out.

In principle, one pressure measuring element is sufficient, said elementbeing arranged between the inhalation and exhalation valves, e.g. in theconduits 7, 8, 11, 12 or 13.

If, on the other hand, the ventilator in question is one in whichpressure is created for instance with a blower, the construction of theventilator can be considerably simpler. The above described system, atits simplest, then comprises one compressed gas interface (a blowerwhich can be used for replacing the compressed air interface and thevalve associated with it); the inhalation conduit 7, 8, arranged as anextension to said blower; the pressure measuring elements 20, anover-pressure restrictor valve, a valve allowing breathing from theatmosphere, a directional valve for inhalation, arranged in connectionwith the inhalation conduit; the exhalation conduit 13, including theexhalation valve 24 and a directional valve for exhalation; the Y piece9; the control system 26; and the safety valve 21. With the exception ofthe safety valve 21 and the related control, which will be describedlater, this construction represents conventional technology, so it isnot separately shown in the drawings and it will not be described herein any further detail.

The general operation of a system according to above described FIG. 1,correspondingly, has been already described in detail at the beginningin connection with the description of the prior art, with the exceptionof the safety valve 21 and the related control, so instead of going intothis operation here in further detail, let us now concentrate on thedescription of the safety valve 21 essential to the invention and itsstructure and operation, particularly with reference to a structureshown in FIG. 1.

The safety valve 21 shown in the example illustrated by FIGS. 2 to 4comprises a vertical, elongated valve housing 37, the top part of whichis provided with a ring-shaped flange 38 which is used to attach thesafety valve to the selected ventilator conduit. A closing element 39 isarranged in the housing 37 for a movement parallel to the axis of thehousing 37. The closing element 39 comprises a rod 40 for enabling saidmovement and a valve plate 41 which, when the valve is in a closedposition, seals against a seat 42 of a preferably triangularcross-sectional profile, arranged on the top surface of the flange 38.Within the circle of the seat 42 openings 43 are arranged in the flange38 to allow connection from the selected ventilator conduit to theatmosphere when the valve is in an open position. It is to be noted herethat the seat structure can naturally also consist of for instance alevel surface and a sealing possibly associated with it.

The valve 21 is most advantageously arranged in the inspiration branchof the ventilator, in other words, in the gas mixture and inhalationconduit assembly 7, 8, for instance at the point shown in FIG. 1, in asubstantially vertical position in such a way that the closing element39 seals against the seat 42 by gravitation. This sealing becomes moreeffective by the over-pressure during inhalation. Since the inhalationflow, however, can be turbulent and the over-pressure small, there is arisk of leakage during inhalation. The risk can be reduced by increasingthe mass of the closing element 39, but this increases the breathingeffort, as will be shown later.

To ensure that the valve 21 closes, a first actuator 44, preferably asolenoid reel, is arranged between the housing 37 and the rod 40, saidreel sealing the valve plate 41 against the seat 42 by pulling the valverod 40 downward when an electric current is supplied to the reel 44 vialeads 44a. Since a primary closing force is provided by gravity and byover-pressure during inhalation, the force the actuator 44 exercises onthe closing element 39 can be small. This makes it possible to have anactuator which is small both as regards size and the power required.

Should the pressure during ventilation exceed the over-pressure limitset for the safety valve 21, the control system 26 activates a secondactuator 45. Its function is to lift the closing element 39 from itsseat 42 to release the pressure in the inhalation conduit 8. The secondactuator 45 must be strong, because in a situation of malfunction thepressure in the inhalation conduit 8 can become even as high as the 12kPa mentioned earlier and the closing surface of the closing element 39is large, allowing thus low resistance to spontaneous breathing(described later). In a malfunction situation it is also possible thatthe second actuator has to work against the first actuator 44.

In the example shown in FIGS. 2 to 4 there is, arranged below the rod40, a second rod 46 substantially similar to the former, the secondactuator 45 being then arranged between the second rod 46 and thehousing 37 in a corresponding manner as the first actuator 44. Saidactuator 45 is preferably also a solenoid reel, like the first actuator44. For the above reasons it must, however, be considerably moreeffective than the first actuator 44. When the second actuator 45 isactivated by an electric current supplied over the leads 45a, the secondrod 46 pushes the first rod 40 upward, releasing the valve plate 41 fromits seat, which allows the over-pressure in the inhalation conduit 8 tobe released into the atmosphere. The rods 40 and 46 are described hereas separate elements, although they could also be made into a singleelement (not shown in the drawings). To ensure that after the secondactuator 45 has been released, the situation will return to normal asquickly and securely as possible, between the flange 47 arranged at thebottom end of the rod 46 and the second actuator 45 is arranged a spring48 forcing the rod 46 downward. Said spring 48 is, however, notnecessary.

The releasing of the closing element 39 can also be performed by meansof a pressure medium received from either of the tanks 1, 4 (FIG. 1).This can take place by the pressure medium being supplied through apressure connection arranged in the opening 49 on the lower surface ofthe valve housing 37 in such a way that the pressure acts on the flange47. The flange 47 must then naturally be sealed against an inner surface50 of the housing 37. Other parts of the construction can remain asshown in FIGS. 2 to 4 or in FIG. 5, in which the actuator 45 has beenremoved. In the case shown in FIG. 5 the valve housing 37' and the rod46' can be shorter than those in FIGS. 2 to 4 due to the actuator 45being removed.

A shortcoming of the compressed air solution is, however, that in somespecial cases only one of the pressure tanks 1, 4 is connected. If thena malfunction occurs that requires the safety valve 21 to open, it doesnot open unless it has been connected to another pressure source.

Spontaneous breathing from the atmosphere through the safety valve 21provided with the actuators 44 and 45 becomes possible when both theactuators are released, which happens automatically for instance whenthe ventilator is not connected to power mains or it looses theelectrical driving force for one reason or another. The under-pressurecreated by the patient's inhalation then causes under-pressure also inthe inhalation and exhalation conduits 8 and 13. Said under-pressurecauses the directional valve (not shown in the drawings) of theexhalation conduit 13 to close and the closing element 39 of the valve21 of the invention to open. Since the valve is located in the gasmixture and inhalation conduit assembly 7, 8, inhalation is performedover said assembly from the atmosphere through the openings 43 in thevalve 21. The under-pressure that the valve 21 requires in order to opendepends on the weight of the closing element 39. To minimise breathingeffort, the mass of the closing element must therefore be as small aspossible. The over-pressure caused by exhalation in the inhalationbranch 7, 8 and, on the other hand, the mass of the closing element 39in turn cause the valve 21 and thus the whole inhalation conduit toclose. Since the over-pressure can be small, the weight of the closingelement 39 must be sufficient for exceeding the friction forces actingon it. The same over-pressure also acts on the exhalation conduit 13 andon the directional valve therein by opening it. The two directionalvalves in the system, i.e. the actual safety valve 21 and thedirectional valve for exhalation, thus effectively prevent returnbreathing.

The safety valve 21 of the invention therefore constructionally providesan over-pressure restrictor valve and a valve enabling breathing fromthe atmosphere and, mainly operationally, a directional valve forinhalation, said valves being monitored and controlled by the abovedescribed control system 26, which receives its most important controldata from the pressure measuring element 20. In the case of twoactuators, the path 36 from the control system 26 comprises separatecontrol settings for each actuator.

Other alternative embodiments of a safety valve of the invention areillustrated in FIGS. 5 and 6. The safety valve 21' shown in FIG. 5 isotherwise similar to the one shown in FIGS. 2 to 4, except that thesecond actuator 45 is removed and fully replaced by the use of apressure medium, which allows the housing 37' to be made very short.This solution requires that the valve 21' must always be connected to apressure medium source to ensure that it functions under allcircumstances. A hose 51 from the pressure medium source (not shown inthe Figure) is attached to a bottom opening 52 of the safety valve 21'and said hose is provided with a valve 53 which is controlled with itsown control settings provided by the above described control system 26.It is to be noted here, too, that the described spring 48 is notabsolutely necessary. This construction could be further simplified byremoving, in addition to the spring 48, also the rod 46' and byreplacing them with a moving diaphragm, arranged below the rod 40 andsealed from its edges to the housing 37' in such a way that between thepressure joint of the diaphragm is arranged a sealed chamber. Thepressurisation of this chamber thus leads to the opening of the valve21'. The diaphragm solution is not separately shown in the drawings.

In a solution according to FIG. 6 the actuators and the lower part ofthe construction, in turn, are like those in FIGS. 2 to 4, whereas theclosing element 39" and the seat structure 42" are different. In thissolution the closing element 39" comprises a closing ball 41", whichco-operates with a cone-type socket surface 42" of the cone 38" to openand close the openings 43". The closing ball 41" could here be alsoreplaced by a suitable cone structure not shown, however, in thedrawings.

The safety valve 21'" of FIG. 7 differs from the other solutionsdisclosed in FIGS. 2 to 6 in that the functionality is achieved withonly one bi-directional actuator 54. The actuator 54 comprises apermanent magnet 55 and a coil 56 mounted with the valve housing 57. Thecontrol system 26 can supply electrical current into the coil in bothdirections. This makes the magnet-coil system 55, 56 either pull or pushthe valve arrangement 59, 39'". An advantage of this single actuatorsystem compared with double actuator systems is that in the case of anysingle malfunction the actuator does not need to act against anotheractuator force. Another advantage of the device is its smaller size andsimpler mechanical construction.

In the case shown in FIGS. 2 to 4 the lower surface of the closing plate41 and/or the surface of the seat ring 42 can also be provided with asoft sealing layer or an element made e.g. of rubber to improve thesealing. The same is also valid for the solution shown in FIG. 7. A sametype of additional sealing can also be considered in connection with theclosing ball 41" and the cone surface of FIG. 6. These solutions havenot been described in the drawings.

The above description is only an example of the invention and only meantto illustrate the invention. A person skilled in art can, however,implement the details of the invention in various alternative ways. Sofor instance a closing element of a valve of the invention and itscounter surface can be provided in a number of different ways. The onlyessential feature is that it opens and closes according to theprinciples described above.

We claim:
 1. A ventilator for intensified breathing, said ventilatorcomprisingat least one compressed gas interface for inhalation gas, aninhalation conduit connected to the compressed gas interface for theinhalation of said gas, pressure measuring elements for inhalation gas,said elements being arranged in connection with the inhalation conduitor a space having a flow connection thereto; a restrictor valve for anover-pressure in the inhalation conduit; a valve arranged in theinhalation conduit, said valve allowing breathing only from theatmosphere through the inhalation conduit; and a directional valve forinhalation, arranged in the inhalation conduit, an exhalation conduitfor exhalation gas, including an exhalation valve and a directionalvalve for exhalation, and a control system, which controls theover-pressure restrictor valve on the basis of the pressure measurementof the inhalation gas, whereby the over-pressure restrictor valve andthe valve that makes breathing from the atmosphere possible are combinedto provide a safety valve, which is arranged to be controlled by saidcontrol system and which comprises a closing element; means at least foropening the closing element; and a connection to the atmosphere, saidconnection being possible to open and close by said closing element,characterized in that the closing element is arranged in the safetyvalve in such a way that it remains in a closed position at least partlyby the impact of gravity, whereby said safety valve also provides adirectional valve for inhalation, which closes during exhalation theconnection to the atmosphere.
 2. A ventilator according to claim 1,characterized in that it comprises only one compressed gas interface,which is provided by a blower.
 3. A ventilator according to claim 1,characterized in that the pressure measuring elements are locatedbetween the inhalation and exhalation conduits.
 4. A ventilatoraccording to claim 1, characterized in that it comprisesa compressedoxygen interface, including compressed oxygen conduits, provided with apressure tank, a compressed air interface, including compressed airconduits, provided with a pressure tank, a gas mixture conduit where theflows from compressed oxygen and compressed air conduits are combined.5. A ventilator according to claim 4, characterized in thatflowmeasuring elements and inhalation valves are arranged in compressedoxygen and compressed air conduits, oxygen concentration measurementelements are arranged in the gas mixture and inhalation conduitassembly, pressure measuring elements and flow measuring elements arearranged in the exhalation conduit, whereby the control system alsocontrols the inhalation valves and the exhalation valve on the basis ofthe measured pressures and flows.
 6. A ventilator according to claim 1,characterized in that the closing element is arranged in the valvehousing for a substantially vertical movement, whereby the connectionthat can be opened and closed to the atmosphere is located below theclosing element.
 7. A ventilator according to claim 6, characterized inthat the closing element comprises a closing plate, which co-operateswith a seat ring of a substantially triangular profile, and that theconnection to the atmosphere is provided by openings arranged adjacentto the seat ring, inside the ring.
 8. A ventilator according to claim 7,characterized in that the lower surface of the closing plate and thesurface of the seat ring are provided with a soft sealing layer made forinstance of rubber.
 9. A ventilator according to claim 6, characterizedin that the closing element comprises a closing ball, which co-operateswith a cone-type seat surface.
 10. A ventilator according to claim 1,characterized in that it comprises a device that both closes and opensthe closing element.
 11. A ventilator according to claim 1,characterized in that the safety valve comprises the first means forclosing the closing element and the second means for opening the closingelement.
 12. A ventilator according to claim 11, characterized in thatthe second means can open the closing element against a closing forceprovided by the first means and the pressure prevailing in the patientconduit.
 13. A ventilator according to claim 12, characterized in thatthe second means for opening the closing element comprise a partarranged to co-operate with a rod of the closing element, and thatbetween said part and the valve housing are arranged spring means, whichin a normal situation force said part away from the rod of the closingelement.
 14. A ventilator according to claim 13, characterized in thatthe part arranged to co-operate with the rod of the closing elementprovides a piston moving in the valve housing, and that the valvehousing is provided with a pressure medium interface for conveyingpressure medium to a space between a surface of the piston and the innersurface of the valve housing, to open the closing element, said surfaceof the piston facing away from the closing element.
 15. A ventilatoraccording to claim 13, characterized in that the part arranged toco-operate with the rod of the closing element is provided as a secondrod substantially corresponding to the rod of the closing element, andthat between the second rod and the valve housing is arranged the secondactuator, which is more effective than the first actuator.
 16. Aventilator according to claim 15, characterized in that the secondactuator comprises a solenoid arranged round the second rod.
 17. Aventilator according to claim 11, characterized in that the closingelement comprises a rod for its closing and opening movement, that thefirst means closing the closing element comprise a first actuatorarranged between the valve housing and the rod of the closing element.18. A ventilator according to claim 17, characterized in that the firstactuator comprises a solenoid arranged round the rod of the closingelement.
 19. A safety valve connected to a patient conduit of anapparatus for intensified breathing, said safety valve providing in thepatient conduit a restrictor valve for an over-pressure of an inhalationgas and a valve allowing breathing from the atmosphere through thepatient conduit, said safety valve being controllable by a controlsystem connected to it, said control system issuing control commands tothe safety valve on the basis of inhalation gas pressures measured inthe patient conduit and said safety valve comprising a closing element,a valve housing, means at least for opening the closing element and aconnection to atmosphere, said closing element enabling the connectionto be opened and closed, characterized in that the closing element isarranged in the safety valve in such a way that the closing elementremains in a closed position at least partly by the impact of gravity,whereby said safety valve also provides a directional valve forinhalation, which closes during exhalation the connection to theatmosphere.
 20. A safety valve according to claim 19, characterized inthat the closing element is arranged in a valve housing for asubstantially vertical movement, whereby the connection to theatmosphere that can be opened and closed is located below the closingelement.
 21. A safety valve according to claim 19, characterized in thatit comprises an apparatus, which both closes and opens the closingelement.
 22. A safety valve according to claim 19, characterized in thatthe safety valve comprises a first means for closing the closing elementand a second means for opening the closing element, whereby the secondmeans can open the closing element against the closing force caused bythe first means and the pressure prevailing in the patient conduit. 23.A safety valve according to claim 22, characterized in that the closingelement comprises a rod for its closing and opening movement, that thefirst means for closing the closing element comprise a first actuatorarranged between the valve housing and the rod of the closing element.24. A safety valve according to claim 23, characterized in that thefirst actuator comprises a solenoid arranged around the rod of theclosing element.
 25. A safety valve according to claim 22, characterizedin that the second means for opening the closing element comprise asecond rod arranged to co-operate with the rod of the closing element,and that between said second rod and the valve housing are arranged aspring means, which in a normal situation forces said second rod awayfrom the rod of the closing element.
 26. A safety valve according toclaim 25, characterized in that the part arranged to co-operate with therod of the closing element provides a piston moving in the valvehousing, and that the valve housing is provided with a pressure mediuminterface for conveying pressure medium to a space between a surface ofthe piston and an inner surface of the valve housing, to open theclosing element, said surface of the piston facing away from the closingelement.
 27. A safety valve according to claim 25, characterized in thatthe second rod arranged to co-operate with the rod of the closingelement substantially corresponds to the rod of the closing element, andthat between the second rod and the valve housing is arranged a secondactuator.
 28. A safety valve according to claim 27, characterized inthat the second actuator comprises a solenoid arranged around the secondrod.
 29. A safety valve according to claim 19, characterized in that theclosing element comprises a closing plate, which co-operates with a seatring of a substantially triangular profile, and that the connection tothe atmosphere is provided by openings arranged adjacent to the seatring and inside the seat ring.